Conventionally, as etchants for silicon wafers and the like have been used buffered hydrofluoric acids comprising HF (50-wt. % aqueous solution) and NH4F (40-wt. % aqueous solution) at such a ratio that can achieve a desired etch rate.
However, the buffered hydrofluoric acids etch doped oxide films such as BSG (boron silicate glass film), BPSG, PSG (phosphosilicate glass film), AsSg (phosphosilicate glass film) and the like faster than they etch undoped oxide films such as TEOS (oxide film formed by CVD method using tetraethoxysilane gas) and like USG, THOX and like. Therefore, the buffered hydrofluoric acids can not etch the doped oxide films and undoped oxide films at the same rate.
An object of the present invention is to provide an etching solution and an etching method for etching undoped oxide films such as TEOS, THOX and the like and oxide films doped with impurities at the same rate.